1958 RCA 14-PD8057 Horizontal Issues/Circuit Board Nightmares

[Chris K]

Hi folks. Working on one of these very popular B&W portables. I've restored and sold several but this latest project is giving me some fits to say the least. Anyone who has worked on one of these knows the circuit board was not designed with service in mind. It's mounted and shielded like a bank vault. The board itself is grounded in six places to the chassis frame it sits on...the 4 corners and for good measure, a spot in between on the 2 long sides. Additionally, there's an RF shield about half an inch under the board covering the entire thing that's screwed to the mounting frame and has almost inaccessible tabs soldered to points on the traces of the circuit board in 4-5 places. There are some access openings but they are not solder iron friendly for sure. Removal of the CB is not a practical thing to do given it's situation and the soldering and presence of many wires on the top of the board. For this reason, most of the work I do on these TVs is top of the CB component replacement. The power supply is so much easier to service.

So given this, the TV has a NOS 14ATP4 CRT that's bright and crisp. It has issues with a jumpy and distorted horizontal circuit so I was attempting to adjust it by turning the core in the horizontal waveform coil mounted to the dreaded CB. Just as I was getting close, the core crumbled. I was able to get a NOS Miller 6337-R direct replacement for it. I think I'm just going to clip off the broken coil and solder the new one in by attaching it to the metal tab remnants on top of the board instead of diving into hell on the underside.

Stay tuned. I'm all but certain I'll create more issues than I solve!

[Alex KL-1]

Good luck, somo old PCB are really fragile, besides the dreaded chassis tank-like-soldered as you said...

[Chris K]

Thanks...already have an issue! The NOS coil has 3 tabs like the original. If I'm reading the description that came in the box and looking at the coil itself, tabs 1 and 3 are the ins and outs of the coil winding. What would tab 2 be...a ground??? I don't see that depicted in the schematic. Anyway, here's the schematic of the horizontal circuit part where the waveform coil resides.



So from the looks of it, I connect pins 1 and 3 to the leads going to the 0.01uF capacitor on the board?

I did this and now...no picture or horizontal signal. I checked it at the horizontal hold control with my scope and nothing. No horizontal waveform and no picture. Now, as most of you know, this is probably an idiotic screw up on my part...a tube knocked loose, a bad solder joint etc....Before the replacement of the waveform coil, I had a picture that was sharp and bright, just unstable and distorted horizontally

I guess my question is could a mis-wired waveform coil completely eliminate the horizontal signal coming out of the oscillator or should I still have the signal at W11 even if it's not wired correctly or is missing? If it could affect the horizontal signal from the 8CG7 and I remove the new coil, should I get a double peaked horizontal trace at W11 and does removing it seem like a good troubleshooting strategy?

[Yamamaya42]

Originally Posted by Chris K

Thanks...already have an issue! The NOS coil has 3 tabs like the original. If I'm reading the description that came in the box and looking at the coil itself, tabs 1 and 3 are the ins and outs of the coil winding. What would tab 2 be...a ground??? I don't see that depicted in the schematic. Anyway, here's the schematic of the horizontal circuit part where the waveform coil resides.



So from the looks of it, I connect pins 1 and 3 to the leads going to the 0.01uF capacitor on the board?

I did this and now...no picture or horizontal signal. I checked it at the horizontal hold control with my scope and nothing. No horizontal waveform and no picture. Now, as most of you know, this is probably an idiotic screw up on my part...a tube knocked loose, a bad solder joint etc....Before the replacement of the waveform coil, I had a picture that was sharp and bright, just unstable and distorted horizontally

I guess my question is could a mis-wired waveform coil completely eliminate the horizontal signal coming out of the oscillator or should I still have the signal at W11 even if it's not wired correctly or is missing? If it could affect the horizontal signal from the 8CG7 and I remove the new coil, should I get a double peaked horizontal trace at W11 and does removing it seem like a good troubleshooting strategy?

looking at the paperwork from the box, pin 2 = NC , No Connection, so it's just there to keep the thing stable.
https://www.ebay.com/itm/195881922845
You should be able to do a resistance test from pins 1-3 on the new in circuit and it should be rather close to the one that was removed.

[Chris K]

I did...it ohmed out at 50 ohms between pins 1 and 3. Schematic says 48ohm. I think I did something stupid. I'll go back to basics tonight and make certain the tubes were put back in the correct sockets, that they didn't get messed up internally, seated well...that kind of stuff

[Chris K]

BTW, that's my purchase you see in the eBay link! I've bought a number of NOS RF and IF coils from him in the past. Pretty impressive stock.

[Yamamaya42]

If you look at page 23 of the SAMS, where is has the horizontal oscillator sweep setup, the first step is to put a jumper across that coil, and since the plate of horizontal oscillator gets power (P6) through that coil, it wont work without it, but will if has a jumper.

[Chris K]

Great!!!! Once I eliminate the "stupids" from troubleshooting, I'll try that.

[Chris K]

I'm assuming you have the schematic. If not, I'll post more of the area. The plate of the oscillator gets 175V DC through the waveform coil. Is the drop from 275V to 175V facilitated by R92...the 56K 1W resistor? Just for my education!

[Yamamaya42]

Originally Posted by Chris K

I'm assuming you have the schematic. If not, I'll post more of the area. The plate of the oscillator gets 175V DC through the waveform coil. Is the drop from 275V to 175V facilitated by R92...the 56K 1W resistor? Just for my education!

Yes, as far as I can see, the current path for the Horz Osc V12 pin 6 is R92, up trough L25 (48 ohms), and L24 (20 ohms).
using. https://www.earlytelevision.org/pdf/...sams_396-3.pdf

[Chris K]

OK thanks. Me too, using 396-3 from the ETF.

[Chris K]

Broken trace. Fixed with a jumper. Waveform looks perfect but, I'm only at around 13KC not 15.75 and I can't get the horizontal dialed in. Vertical locks and is fine. Distorted and wild messed up crosshatch off my generator. Three adjustments in the horizontal circuit...width, waveform and horizontal hold. Maybe the oscillator is weak. I'll test it.

EDIT: Looking at the caps in the horizontal. There are 3 mica caps, 2 at 1000pf (C99 C100) and one at 330pf (C98). I didn't replace any of these but someone did replace C99 with a 5% cap but not a mica...at least not that I can tell. It It's a rectangular cap like one of those safety caps and says CD Type Made in USA 5 Amps on the top...5% and "D" printed in quotes on the face. There's more including the uF but there's a bunch of crap in front of it and I can't see it. Definitely not what's depicted in the photo of the board in the Sams.

[Yamamaya42]

Originally Posted by Chris K

Broken trace. Fixed with a jumper. Waveform looks perfect but, I'm only at around 13KC not 15.75 and I can't get the horizontal dialed in. Vertical locks and is fine. Distorted and wild messed up crosshatch off my generator. Three adjustments in the horizontal circuit...width, waveform and horizontal hold. Maybe the oscillator is weak. I'll test it.

EDIT: Looking at the caps in the horizontal. There are 3 mica caps, 2 at 1000pf (C99 C100) and one at 330pf (C98). I didn't replace any of these but someone did replace C99 with a 5% cap but not a mica...at least not that I can tell. It It's a rectangular cap like one of those safety caps and says CD Type Made in USA 5 Amps on the top...5% and "D" printed in quotes on the face. There's more including the uF but there's a bunch of crap in front of it and I can't see it. Definitely not what's depicted in the photo of the board in the Sams.

Why am i having this sudden feeling of dejavu?
cause I just went trough this with my maggy?
C99 looks like it may be just a decoupling capacitor, not sure.
Critical one are C94,C95,C96,C98 and the resistors in the area, C93 passes the sync pulses down from the sep amp, so if it's not right you won't have lock or weak lock, C100 passes the signal to the output, the problem is prob in a the AFC area, if the caps or resistors are bad / out of spec, it's not allowing the PLL circuit to work correctly and thus out of frequency.

[Chris K]

Not to fixate on C99 but I was able to move things around a bit and it looks like the cap is a 0.01uf cap and not 1000pf. C93 on my CB is a ceramic cap but I can't make out the rating. Supposed to be 82pf. I do have an 82pf mica I could substitute for it. I really don't have any way to test the ceramic. Externally it looks fine. There is another ceramic next to it that's not in the Sams Photo or component list so there might be different versions of this model.

[Chris K]

Actually I can see the 82 in the photo